1. Field of the Invention
The present invention relates to a dental explorer device for detecting caries and periodontal disease using optical coherence domain reflectrometry.
2. Description of Related Art
There are no technologies currently available for producing cross-sectional images of dental microstructure for detection of tooth decay or reliably quantifying the soft tissue changes that occur in gingivitis and periodontal diseases. Diagnoses of disease state are usually made using mechanical probing, visual or tactile examination, and radiographic imaging. Visual inspection alone is effective only for gross lesions where serious tooth decay has occurred. A common method to probe for caries, or tooth decay, is visual and tactile examination, specifically direct observation using a dental explorer. The tooth is visually examined and tactilely explored to determine the presence of indicators of tooth decay such as surface irregularities, crevices, or discoloration. However, the practice of probing all accessible tooth surfaces with a sharp explorer is coming under increased scrutiny since it can further damage enamel already weakened by decay and may also cause cross-contamination between teeth.
Since tooth decay primarily affects the region of calcium below the tooth surface, detection of caries before significant damage occurs in the tooth is very difficult. By the time caries is evident under visual and tactile examination of the tooth, the disease is usually in an advanced stage, requiring a filling and occasionally leading to tooth loss. As a consequence of conservative diagnoses and treatment, there are false positives leading to unnecessary drilling and placement of restorations in healthy teeth. Currently there is no device for accurately determining whether restorations are in need of replacement, resulting in enormous costs for unnecessary replacement of good restorations and complications such as root canals from not replacing defective or aged restorations.
Radiography is often used for detection of cavities, since it provides integrated views of tooth structure that in certain orientations can isolate carious lesions. The sensitivity of radiographic systems, however, is limited by visible changes in film density, making identification of small carious or precarious regions difficult. Since radiographs are two dimensional, precisely locating the position of such decay is impossible. Moreover, due to the orientation of the x-ray imaging, only interproximal lesions (between the teeth) are easily detected, while occlusal lesions (top of the tooth), are difficult to detect unless they are very large. In addition, radiography uses harmful ionizing radiation and provides no information on soft tissue state. Periodontal disease cannot be identified until significant bone loss has occurred.
To detect periodontal disease, mechanical probes are placed between the soft tissue and tooth to assess the condition of the tissue. The depth of probe penetration is measured, and the attachment level is estimated from a fixed reference point on the tooth. These probes can be painful for the patient and have several sources of error resulting from variations in insertion force, inflammatory status of tissue, diameter of probe tips, and anatomical tooth contours.
Given the disadvantages of current detection techniques, a need clearly exists for a device that can provide early, safe, and painless diagnosis of caries and periodontal disease. Only when the progression of caries is detected early can restorative dentistry be effective. The present invention provides such a device and applies the optical techniques of optical coherence domain reflectometry and optical coherence tomography to image dental tissue and detect the presence of caries and other problems.
Optical coherence domain reflectometry (OCDR) was developed as a high resolution ranging technique for characterization of optical components and was based on bulk optics. See Youngquist et al., "Optical coherence-domain reflectometry: a new optical evaluation technique", Optics Letters 12(3):158-160 (1987). The first fiber optic based OCDR system was constructed by the U.S. National Bureau of Standards for micro-optic technology. See Danielson et al., "Guided-wave reflectometry with micrometer resolution", Applied Optics 26(14):2836-2842 (1987).
OCDR uses a low coherence Michelson interferometer to probe the sample, generating reflection signals as a function of depth. When the probe beam is transversed across the sample, a series of axial scans can be stacked together to form a high-resolution two-dimensional optical coherence tomogram. See Lee et. al, "Profilometry with a coherence scanning microscope", Applied Optics 29(26):3784-3788 (1990). Optical coherence tomography (OCT) was developed to produce cross-sectional images of biological microstructure by combining transverse scanning with a fiber optic OCDR system. See Huang et al., "Optical Coherence Tomography", Science 254:1178-1181 (1991). U.S. Pat. No. 5,321,501 discloses the general means for construction of an OCT system, specifically as it applies to OCT imaging of the eye for diagnosis of ocular diseases. U.S. Pat. No. 5,459,570 discloses OCT imaging of biological tissue, including measurement of tissue optical properties and tissue birefringence. These OCT devices provide imaging in the eye and circulatory system.
The application of OCT for dental applications was pioneered by the University of California at Lawrence Livermore National Laboratory. U.S. Pat. No. 5,570,182 discloses the use of OCT for diagnosis of dental caries and periodontal diseases. The ability of OCT to produce in vivo images of clinically relevant biological microstructure in has been demonstrated clinically by the applicants. See Colston et al., Optics Express 3:230-238 (1998).
In order for OCT to be practical and convenient to clinicians for use on patients, it would be advantageous to package a hand-held, portable OCDR dental explorer or mechanical probe device for non-invasively evaluating the health of dental tissues. The present invention uses a fiber optic inserted in a standard dental explorer or mechanical periodontal probe, designed to replace conventional, non-imaging counterparts. These improved devices can safely and accurately collect in vivo, intraoral OCDR and OCT images of dental tissue and microstructure for evaluation of dental health.